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So long as I have time... I will use this as a teacher. The students you watch over, I will watch them myself. No matter what, these tentacles will not let them go.
~ His vow to Aguri after her death.
The tentacles spoke to me, asked what I wanted to be. To be weak I said, to be flawed, vulnerable. To perceive weakness in others not to exploit but to protect. To be a guide, to be a teacher.
~ Korosensei's goal.
~ Korosensei in shock and embarrassment.

Korosensei is the homeroom teacher for Class 3-E of Kunugigaoka Junior High School, and the supporting protagonist of Assassination Classroom. He claimed to be responsible for creating the permanent crescent moon and said that he planned to destroy the earth after "teaching" Class 3-E for a year. Prior to being a teacher, he was the master assassin known as the 1st "Deity of Death" until he was betrayed by his apprentice and captured, then used in experiments that gave him a new appearance and powers.

While he was captive, he was assigned to be monitored by Aguri Yukimura, the original homeroom teacher of the Class 3-E of Kunugigaka, with whom he falls in love with. When his attempt to escape the lab he was imprisoned results in her death, he promises to use his new powers for good and honor her memory for the remaining year he has of life by becoming the new teacher of 3-E, in order to guide and watch over her students.

In the Japanese version, he is voiced by Jun Fukuyama, who also voiced by Lelouch vi Britannia from Code Geass series, Joker from Persona 5 and Roy from Fire Emblem video game series. Tomokazu Seki in the OVA and Masaya Onosaka in the VOMIC version of the show.

In the English version, he was voiced by Sonny Strait in all anime appeances.



  • Jun Fukuyama (anime series and 3DS Game)
  • Tomokazu Seki (OVA and J-Stars Victory VS)
  • Masaya Onosaka (VOMIC)
  • Kazunari Ninomiya (live-action)


  • Sonny Strait


Korosensei's original appearance is of a human with small black eyes, short dark hair and pale skin. While working as an assassin, he would wear dark colored clothes, usually black or brown.

After being used in experiments, Korosensei acquired the appearance of a yellow bipedal octopus. He is about three meters tall and possesses a large, bulbous head with a large smile and small, beady eyes. He uses two feelers as arms, with two fingers each, and utilizes the rest of his tentacles to walk with. According to Korosensei himself, his nostrils are so small yet when discovered, it seems that he has four eyes.

Korosensei wears a black academic dress, a small black square academic cap with a yellow tassel, and a large black tie with a yellow crescent-shaped moon on it.

He seems to make a habit of dressing in formal clothing. After being taken prisoner by Yanagisawa, he was put in patients' scrubs until his escape.


It was revealed that he was raised in an environment "where everybody could easily betray one another to the point that one could only trust oneself". Through these hardships, he decided to become an assassin in order to survive. Despite he gained an apprentice, he only saw him as a tool for his goals, which caused the latter to finally betraying his master.

However, after meeting to Aguri Yukimura, he finally knew what compassion really was becoming much more kind and compassionate. According to Aguri, if he was born in a peaceful country, his personality would be "someone a little perverted, with a good head but a few screws loose, petty about small things, and also a lot stubborn... or something like that." He has/would have "a gentle smile not just for business, but because he is a gentle person himself." This prediction happens to reflect his personality which became forefront after he answered the tentacles.

When first introduced, Korosensei is a jovial individual who demands absurd and seemingly mundane requests despite claiming he will be the cause of the planet's destruction in a year. He is also rather kind to others in general and can switch from silly and childish to serious on the fly. According to Nagisa, Korosensei also is unintentionally petty at others at times and loves gossip, both traits heavily noted through the series.

From time to time pieces of his old personality as The Reaper are visible such as when Terasaka tried to sacrifice Nagisa to kill Korosensei, and Korosensei menacingly threatened all of their families if they tried another self-harming attempt like that. In that moment, he resorted to his old method of teaching through fear. As the series progresses his character development renders him more and more capable of true empathy and learning to use that empathy to teach lessons instead of through fear and reward like he had with his first student.

Korosensei deeply cares for his students' emotional and physical well-being and loses his temper whenever any of them are put in danger, even by one another. On the annual school trip to Kyoto, a few of his students were assaulted/kidnapped by a gang of high schoolers hidden in an alley. After searching the entire area painstakingly, he infiltrated the abandoned building where two kidnapped students were being held at and single-handedly beat up all of the high schoolers and scaring them away.

One of Korosensei's attributes is that he is able to connect to each student individually, being an objective, empathic, and observant person who will do almost anything to help his students. This is the reason why all the students respect him despite the fact that he is going to blow up the Earth in a year. Taking care of each student's needs, Korosensei is sometimes piqued by a student's current problems or interests and tries his best to guide the student along or solve it for them.

Korosensei loves sweets almost to extreme cases, and is also shown to be a very perverted character, a trait he shares with his student Okajima. This characteristic is revealed to be the side effect of the experimentation which made him unable to hide his true feelings.

Powers and Abilities

Antimatter Physiology: Due to the human experiments of produing antimatter in a living body by Shiro, Korosensei's entire appearance is an octopus-like creature with multiple tendrils that are his tentacles. Anything aside Anti-Sensei Weapons will be immune to him. It is initially believed that he will self-destruct by the time of Class E's graduation; however it has since been proven that the chances are minuscule at best

  • Protective Coloring: Korosensei can change any color for his skin and it is used for his disguises and camouflages. It is also the principle of the faces which represents his moods. Since it is only apply on his skin, to fully use the ability Korosensei must be fully naked. Although when he is blushing, the coloring won't cover the blushes on his face.
  • Mucus: The standard trait of an Antimatter organism, the mucus that Korosensei has varied uses for support purposes, such as waterproofing, cleansing, adhesive and the replacement of tears.
    • Liquefaction: After he drank the 4th poison made by Manami Okuda, Korosensei developed an ability to control his fluidity. He can morph into a mass of mercury-like slime. In cost of his massive body and tentacles, Korosensei can fit through any space while retaining most of his abilities. It is unknown that if there are any demerits to over use this ability.
  • Absolute Defense: Another trump card never used until the Okinawa trip, Korosensei can shrink his body into a sphere and the remaining energy from the transformation hardens as a crystallized second layer over his spherical body, making him impervious to harm. After twenty four hours, the external shell liquefies and he will slowly absorb energy over a period of time until he fully regenerates. The only drawback to this in the span of a day, he is rendered immobile and is susceptible to being carried around. The only mechanism might be able to breakthrough this sphere is Lance of the Heavens.
    • Energy Laser: An ability developed from the Absolute Defense. Korosensei can tap a portion of his inner energy to his tentacles in order to create a laser blast from it. It is capable to annihilate the Anti-Sensei Cloth and blast off anything else with scratches barely left over.
  • Molting: A once-a-month occurrence, Korosensei can shed his old skin and use it as a protective membrane either on himself or another individual, protecting them from being hurt even from military-grade explosives. Afterwards, his reaction speed may slow temporarily but he is still fast enough to dodge the assassins of 3-E.
  • Regeneration: If one or more of his tentacles are maimed, Korosensei can regenerate the severed limb like a lizard regenerating its tail. However, this leaves his stamina weakened as his reaction speed is dampened, albeit not enough to topple the teacher.
    • Surgery Skills: After he was unable to save Aguri from fatal wounds, he start learn about medical operation and surgery methods which he first apply it on Azusa to remove her brain tumour without damaging her. Later, he use it to heal and revive Akari (Kayano) from fatal wounds that was caused by God of Death and Yanagisawa after surgery has been completed. Like his Regeneration and Molting, the surgery also can weaken his stamina, which sometimes need to replenish is stamina during the process of the surgery.
  • Superhuman Speed: Korosensei can travel up to the speed of Mach 20. His normally soft and jelly-like head hardens under immense pressure as a process known as the dilatancy phenomenon, which presumably lowers his wind resistance, allowing him to reach inhuman speeds. The only known objects to surpass this are space shuttles which is used for space launch which reaches the speed of Mach 23 and other Advanced-Antimatter Organisms.
    • Superhuman Reflexes: Korosensei can react and dodge multiple fires of Anti-Sensei bullets and move away from any harm. His reflexes also allow him to react fast enough to catch or deflect any flying projectile in mid-air using what he has on hand such as handkerchief or even a chalk. Another example of this is when facing off against Asano Gakuho, he was able to open a test book, solve a denoted question on a small slip of paper and close the book without the explosive contained in the book detonating. Plus, he is also fast enough to molt and toss his protection skin over the principal when a normal grenade detonated point-blank in his face.
    • Speed Replication: Korosensei's amazing speed allows him to seemingly copy himself dozens of times using after-imagery. Not only can each individual after-image maintain a task for extended periods of time, but Korosensei's "speed copies" are all capable of taking on widely-different tasks both individually and simultaneously without confusing themselves. This technique was primarily used by Korosensei to teach all of Class 3-E one-on-one when a difficult test approached, allowing Korosensei to work with each student separately to work on their problem subjects.
  • Superhuman Senses: Korosensei's sensory perceptions are paramount, and can detect even the most minuscule of changes in temperature, light, sound, and smell. Despite having no visible ears or nose, Korosensei has proven to be able to hear things no normal human can pick up on, as well as detect the most minor of aromas, which aided him greatly in evading the assassination attempts of Class 3-E. Korosensei is especially talented in identifying people by their smell, as well as certain materials (such as explosives and poisons). His eyes are also quite keen, and can keep track of objects going thousands of miles per hour without difficulty, as well as detect the slightest of movements that occur quicker than the blink of an eye.
  • Superhuman Digestion: Korosensei can digest anything aside Anti-Sensei weapons His teeth can crush any hard materials. Whether he eats something or it enters his body, he can either molten the food first then eject it, or it will just be digested. Although it is not guaranteed that Korosensei will have no irregulars after what he has eaten, it is usually have no tactical disadvantages if it is not a weakness for him.
  • Genius Intellect: Even before Korosensei gained his powers, he possesses a gifted mind which allows him to learn and understand complex knowledge in a matter of minutes. With his immense intelligence, he was able to single-handedly teach all the subjects and produce amazing results from the bottom of the barrel class of 3-E. Since gaining his speed, Korosensei has become hypercongnitive, and can process information thousands of times faster than the average human being. His incredible mentality combined with his speed also allows him to multitask on up to dozens of jobs at a time (teaching the entirety of Class 3-E individually and then some), all of which seemingly being done simultaneously. Most impressively, he was able to give the assassination AI Ritsu approximately 985 upgrades in less than a single day, completely transforming her, increasing her intellect, and giving her personality and sentience.
  • Assassination: As the original God of Death, Korosensei was considered the world's best assassin prior to being betrayed by his disciple. As a result, Korosensei can combat nearly every assassination utilized by both Class E and professional assassins, showing to be extremely observant and stealthy at planning and execution.
  • Eidetic memory: Korosensei is deduced to have an eidetic memory, as he is able to store all that he has learned and use them to his advantage, which led to him being the strongest assassin in the world prior to his capture. In order to become an educator to class 3E, he has memorized all of the test books in Japan so as to be able to coach his students where their weaknesses lie.


Because of his answer to the tentacles when they questioned him from within, here are the weaknesses Korosensei gained when he became the teacher to class 3E.

  1. When he tries to act cool, his weaknesses show.
  2. He is surprisingly quick to panic.
  3. He is petty.
  4. His punches are weak.
  5. Boobs (Natural weakness).
  6. He is humble and subservient to his superiors at work.
  7. He has no patience for wire puzzles.
  8. He gets motion sickness.
  9. He can't sleep on a pillow other than his own.
  10. He worries about appearances.
  11. He can't handle hot food.
  12. Getting wet (Natural weakness).
  13. Juicy gossip.
  14. Hackneyed plot developments make him cry.
  15. He gets taken in by rumors.
  16. Time right after molting (Natural weakness).
  17. Time right after regeneration (Natural weakness).
  18. His body goes rigid when bathed in a special beam of light (Natural weakness).
  19. When he returns to normal after a serious situation, he gets embarrassed.
  20. He can only draw simple pictures.
  21. Heat fatigue.
  22. He is strict about poolside manner.
  23. He can't swim (Natural weaknesses).
  24. He likes to gossip.
  25. He is weak against the occult.
  26. If he can't gather people, he feels worthless.
  27. Tone-deafness.
  28. He sucks at hiding.
  29. He gets carried away by official positions.
  30. Heart (Natural weakness).
  31. Not related but acts like a doting parent.
  32. Gets insurance to avoid getting hurt.
  33. He doesn't really know what "your own football" means.
  34. He sucks at reporting.
  35. He suffers from road rage.
  36. Restructuring (Natural weakness).
  37. Grabbing all his tentacles at once makes him unable to move (Natural weakness).
  38. Unintentionally adding insult to injury.
  39. Completely oblivious to the mood in moments of high tension.
  40. Class 3-E students: Undeniably Korosensei's greatest weakness. Although students of 3-E class are subtly aware of this, only three students ever made actual attempts to exploit this factor: Karma Akabane, Nagisa Shiota (using themselves as baits), and Ryoma Terasaka (using Nagisa as a suicide bomber the first time, second unknowingly manipulated by Shiro into nearly drowning his classmates, but has redeemed himself since). Exploiting this weakness means one has no qualms of discarding lives of his/her classmates, and even their own.


Korosensei hides certain things from students on his life which was revealed during Assassination Classroom Extras featuring Hotaru as Main Character of the series. Here are the foibles that Korosensei has for his life as an adult.

  1. Painfully narcissistic designs.
  2. His room resembles a dumpster.
  3. He only makes petty wagers.
  4. A bit of degenerate octopus.
  5. His purpose has shifted from using porn magazines to collecting them all at this point.
  6. Starts a nights off with Cassis and Orange.
  7. Takes forever to decide on appetizer.
  8. Really can't hold his liquor.
  9. Kind of like an old geezer.

In other media

J-Stars Victory VS

Korosensei is notably the only character from Assassination Classroom to appear as one of the playable characters in the anime crossover fighting video game J-Stars Victory VS.

Weekly Shōnen Jump Jikkyou Janjan Stadium

Korosensei appears as one of the playable characters in Weekly Shōnen Jump Jikkyou Janjan Stadium, a free anime crossover fighting mobile game for Android and iOS developed by Konami.


My sweet young assassins. As you ready yourselves to snuff out a life. You understand better than anyone the value of what's lost. Because you've studied, fretted. Turned it over and over in your mind. And in the process without even realizing it, gave that life meaning. It's been a privilege watching you grow. But, the best part was growing right alongside you. So please, in this moment, let me be the finest expression of your blood lust. If I die knowing I've helped these twenty-eight souls find a brighter future. I die exquisitely happy. All things considered, I'd say it's been an exceptionally fun year. I say this with all sincerity. It's a privilege to be assassinated by you. As a fellow spirit, from one traveler to another. Give a yell for all life and strike.
~ Korosensei before being killed.
Hello, how are you? So, I'm the one who blew up the moon, next year I intend to do the same thing to planet Earth, but never mind that now, I'm gonna be your new teacher. Isn't that exciting?!
~ Introduction to Class 3-E.
~ Korosensei in shock and embarrassment.
So long as I have time... I will use this as a teacher. The students you watch over, I will watch them myself. No matter what, these tentacles will not let them go.
~ His vow to Aguri after her death.
The fact that I'm targeted by everyone is proof that I'm powerful, after all.
~ To Nagisa Shiota.
For Sensei, assassination is education. The sensei of the Assassination Classroom becomes stronger as he teaches.
~ To Itona Horibe
I want... to be weak.
~ To his tentacles about himself.
My dear student... may you graduate... in peace.
~ To his fallen apprentice.
The difference between the novice and the master is that the master has failed more times than the novice has tried.
~ Korosensei.
You didn't let emotions or background cloud your judgement... and evaluate me solely on my aptitude as a teacher. Such a proposal is the happiest report card you could have given me.
~ To Gakuho Asuno on Valentines' Day.
If I'm going to be killed, it can't be at the hands of anyone else. I want to be killed by you.
~ To Class 3-E after telling his past.
The tentacles spoke to me, asked what I wanted to be. To be weak I said, to be flawed, vulnerable. To perceive weakness in others not to exploit but to protect. To be a guide, to be a teacher.
~ Korosensei's goal.
As you go through life, the mighty current of society is bound to get in your way, and there will certainly be times things don't go as you'd hoped. When this happens, do not look to society for a cause. Do not renounce society. Frankly, you'd be wasting your time. Instead, just say, "That's life!" and muddle your way through with frustration.
~ To Class 3-E.
You may be exceptionally strong, but I'm exceptionally CLEVER!!
~ To Itona Horibe in their first duel.
To a young person to whom everything comes easily, the pain of defeat can be a much needed wake-up call.
~ Korosensei after disciplining Karma Akabane.
On the surface, the whole concept of exams may seem arbitrary, but deep down, it's not about grades. It's about rising to the occassion. It's about tasting the rapture of triumph and disgrace of failture! They go hand in hand, you see. One is meaningless without the other. To win, one has to lose!
~ Korosensei.
Um, er, The Reaper has a knife, no, wait! It's a wire! He tried to strangle Mr. Karasama, oh wow! Karasama parries and does the... thing, and The Reaper stops him but then Karasama comes in and, oh wow! This is so wow! What a stupendous fight! STUPENDOUS!
~ Korosensei's weakness of terrible narration skills.


  • His name, Korosensei, is a combination of the words 殺せない (koro, 殺せない) which means "unkillable" and the word 先生 (sensei, 先生) which means teacher. This name was given to him by Kayano, both in the original and in the RPG spinoff Koro-Sensei Q!
  • Korosensei was called "Stupid Chicken Pervert Octopus" during class 3-E training using code names, rather than the code name he suggested, 'the imperial prince of fate of the eternal wind'.
  • It is revealed that Korosensei has never actually known his real name.
  • Korosensei is usually represented by a octopus due to his appearance of his head and tentacles. He has self awareness of it as he often draws octopus mascots while scoring exam marks and make jokes about octopus.
    • He also has a nature similar to octopus, as he is highly intelligent for his survival skills.
    • His ability to regenerate his tentacles, healing others, bestowing wisdom, and octopi appearance is a reminiscent of the Akkorokamui.
  • In the popularity poll in Volume 12, Korosensei was ranked 3rd.
  • Korosensei is ambidextrous, being able to write/perform a task with either hands, and being able to work with both hands at the same time.
  • His motto is "Learning and killing are of one body."
  • According to Aguri, Korosensei is not Japanese.
  • His weaknesses for boobs was already seen when Aguri shows him her ogre themed thumb top which Aguri remark him as a pervert even before tentacle ask him for what he want to be making boobs as the only natural weaknesses.
  • When his tentacles asked him what he wanted, Korosensei's response was: "I want... to be weak".
  • His necktie is a present from Aguri Yukimura. Though, the crescent moon motif is his own design.
  • In chapter 136, he disguised as university professor.
  • Korosensei is potrayed by Jun Fukuyama, who previously potrayed another manipulative protagonist, Lelouch vi Britannia's from Code Geass series.
  • He also is one of the most popular and recognizable Anime Heroes, in addition to being one of the primary members of the Shōnen Jump franchise. The reason why he is notably the only character from Assassination Classroom to become one of them is mainly because of some of his anime references that he has done.
  • Many of Korosensei's weaknesses are meant to be ironic. Some examples are that he has motion sickness even though he can move at mach 20, can't swim or get wet, and sucks at reporting despite having the time to change clothes, make tea, and build a large sand castle in half a minute, which are all ironic.